1. Field of the Invention
This invention concerns an inflatable safety bladder for use as a casing safety device for preventing tools from falling into well casings and for venting downhole gases to a safe distance above the top of the well casing. The safety device can be used with water wells or any other opening in the ground around which people work.
2. Discussion of the Prior Art
When oil or gas wells are drilled, a well casing is usually inserted into the hole to prevent the walls of the hole from collapsing. This casing also provides a conduit through which oil and gas is conveyed from subterranean areas to the surface of the ground. A variety of mechanical tasks are performed near the mouth of the casing with small tools such as wrenches and it often happens that these tools slip into the casing and fall to the bottom of the well. When this happens, it is necessary to interrupt the drilling operation and use special devices to fish the tool out of the casing. Such interruptions are costly, inefficient, and time-consuming.
Another problem experienced by persons working near the open mouth of the casing is that explosive or otherwise dangerous gases sometimes seep into the casing, rise to the surface, and are expelled through the open mouth of the casing. If, for example, a worker is using a welding torch near the open mouth of the casing and an inflammable gas is at the same time being expelled from subterranean levels, a fire or explosion often occurs.
No prior art devices have been suitable for preventing the dropping of tools into the well casing or for venting dangerous gases to a safe distance above the open mouth of the casing. For example, U.S. Pat. Nos. 2,629,446, 2,681,706, 3,039,533, 3,393,744, 4,406,461 and 3,493,045 all disclose inflatable drilling hole packers which are placed deep in a hole which has been drilled to seal the hole and prevent the egress of oil and gas from the hole. Because of their placement deep in the hole, they are unsuitable for preventing tools from dropping deep into the hole. These packers are also adapted for use only in the hole, and not in conjunction with a well casing. The packers of these patents are high pressure vessels which are designed to withstand the enormous forces exerted by subterranean oil and gas formations, and are accordingly quite differently constructed than the low pressure bladder of the instant invention. Another drawback of these prior art bladders is that none of them provide a means for venting fluids from the downhole side of the bladder to a safe distance above the open mouth of the casing.
Accordingly, it is an object of this invention to provide a casing safety device for preventing tools from falling into a well casing.
It is also an object of the instant invention to provide a safety device for venting downhole gases or other fluids to a safe distance above the open mouth of the well casing.
It is further an object to provide a low pressure bladder which is relatively inexpensive to construct and easy to inflate.
Another object of the invention is to provide a semi-rigid shroud between the open mouth of the casing and the inflatable bladder to reduce the velocity of falling tools and prevent them from puncturing or damaging the bladder.
It is also an object of the invention to provide a bladder which is designed for placement adjacent the open mouth of the well casing so that tools dropped into the casing can be retrieved merely by reaching into the open mouth and pulling the tools out manually without the necessity for using fishing tools.